Method and apparatus for monitoring melt spinning

ABSTRACT

Meter and booster pump motors are resiliently mounted to deflect or pivot about their own axes in reaction to torque transmitted to their respective pumps. This deflection or pivotal motion is a measurement of the pressures developed by the pumps, and permits early detection of excessive or insufficient pack pressure, inadequate melt supply, etc.

Unit .111

US. Cl. 264-40 6 Claims ABSTRACT UF THE DISCLOSURE Meter and booster pump motors are resiliently mounted to deflect or pivot about their own axes in reaction to torque transmitted to their respective pumps. This de flection or pivotal motion is a measure of the pressures developed by the pumps, and permits early detection of excessive or insufiicient pack pressure, inadequate melt supply, etc.

This is a continuation of copending application Ser. No. 42,102, filed lune 1, 1970, and now abandoned.

The invention relates to a method and apparatus for melt spinning polymer. More particularly, it relates to a method and apparatus for determining the condition of a spinning system by observing the deflection of a resiliently mounted pump motor.

In melt spinning of synthetic fibers it is customary to pump a metered stream of fiber-forming viscous polymer through a spinning pack just prior to extrusion through a spinneret. Various abnormal conditions can occur in such a system, such as plugging of the filter media in a spinning pack, development of channels through the filter media, pack leaks, variation in supply of the molten polymer, etc. Early detection of these defective conditions permits substantially more efficient and economical operation of the spinning unit. One prior art approach to determining such abnormal operation is to mount a mechanical torque gauge on the pump drive shaft. However, it is very difficult to keep mechanical gauges properly calibrated, and since the gauge rotates with the pump shaft, it is difiicult to read and could pose a safety hazard.

Considerable improvement over the rotating gauge was achieved by Nicholson 3,475,523, which discloses accomplishment of the desired result by monitoring the power consumed by the meter and booster pump motors. The operation of Nicholson is generally satisfactory, although it involves certain disadvantages. With the usual motors used to pump molten nylon, the initial wattage signal available under the Nicholson approach is small, in the range of 15-50 millivolts. The novel approach of the present invention makes a much larger initial signal available.

Accordingly the primary object of the invention is to provide a method and apparatus for reliably and accurately detecting certain abnormal spinning conditions. A further object is to provide a method and apparatus of the above character wherein the detection is accomplished by monitoring the deflection of resiliently mounted pump motors. Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a more complete understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic vertical sectional view of an exemplary melt spinning apparatus according to the present invention;

FIG. 2 is a fragmentary end view of the booster pump motor shown in FIG. 1;

FIG. 3 is a graph of spun denier as a function of pack pressure for a particular spinning apparatus;

d States Patent 3,75l,533 Patented Aug. 7, T073 FIG. 4 is a graph of meter pump pivotal displacement as a function of pack pressure for this particular spinning apparatus.

FIG. 1 illustrates a generalized melt spinning apparatus wherein polymer flake is introduced into an aperture (not illustrated) in the top of heated block assembly 22. The flake is melted by heated fins 2 4 and falls as molten polymer into melt pool 26 beneath fins 24. Booster pump 28 is driven by alternating current motor 30, which may be of the induction type. Pump 28 is submerged in melt pool 26 and supplies molten polymer to distribution passage 32. Close-tolerance meter pump 34, driven by synchronous motor 36, has its inlet passage connected to receive the polymer in passage 32, and pumps a metered output stream into chamber 38 for extrusion through spinneret 40. In actual practice several metering pumps would normally be supplied from distribution passage 32. The molten polymer extruded through spinneret 40 is illustrated as forming a plurality of filaments 42 which are solidified or cooled by conventional means (not illustrated) and gathered into yarn 44.

A filter or spinning pack 46 is mounted in chamber 38 above spinneret 40 to remove gel particles and the like from the molten polymer. Filter 46 also imparts desirable shear to the polymer just prior to extrusion, as is well known in the art. Filter 46 may be composed of layers of various grades of sand, stacked screens, sintered porous structures, or the like.

According to the invention, motors 30 and 36 are resiliently mounted for pivotal deflection about their output shafts in reaction to the torque transmitted to their respective pumps. This pivotal movement or deflection is a measure of the pressure developed by the pumps, and therefore is a measure of the condition of the spinning system. Still referring to FIG. 1, the housing or stator frame of motor 36 is bolted to adapter 48. Adapter 48 includes an integral right circular cylindrical extension 50, coaxial with and surrounding output shaft 52. A large bearing 54 is mounted in stationary frame member 56, and supports extension 50 for pivotal movement about the axis of shaft 52. Motor 36 is thus cantilevered, being supported by extension 50 journaled in bearing 54.

As shown in FIGS. 1 and 2, bracket 58 on frame 56 supports the lower end of coil spring 60 adjacent adapter 48. Finger 62 on adapter 48 engages the upper end of spring 60. As illustrated in the drawings, when shaft 52 rotates counterclockwise as viewed from pump 34, the housing or stator frame of motor 36 rotates clockwise with respect to bracket 58 in reaction to the torque developed by the motor. This clockwise deflection or rotation of the stator frame urges finger 62 against the upper end of spring 60, compressing spring 60' by an amount proportional to the torque developed by motor 36.

During normal operation of the FIG. 1 system, as filter 46 traps and removes gel or other impurities, the resistance presented by filter 46 slowly increases and therefore the pressure in chamber 38 increases. This continues until the denier of the spun yarn decreases below acceptable quality control levels because of increased slippage in pump 34, or until a leak develops. If the filter is replaced before the pressure builds up to this critical level, a considerable reduction in production of olf-grade or defective low denier yarn is achieved since the spinning unit may spin oifgrade yarn for many hours before the defective condition is detected by actual measurement of the yarn denier.

FIG. 4 shows displacement of finger 62 in arbitrary units as a function of the pressure in chamber 38 (pack pressure). With the particular apparatus used to derive FIG. 3, 1000 psi. pack pressure corresponds to approximately 16.5 inch-pounds of torque. With pack 46 removed, about 8 inch-pounds torque were required to pump the polymer.

3 With a fresh pack installed, the torque was about 36 inchpouuds, and increased substantially linearly with pressure to a torque of about 107 inch-pounds at 6000 pounds per square inch pack pressure.

Deflection of motor 36 and consequently the developed torque may be detected in many ways, as by a simple calibrated scale situated behind finger 62. With such an arrangement, finger 62 becomes a pointer cooperating with the scale to indicate the developed torque. Similarly, arm 62 can actuate various transducers, which may be electromechanical if desired. Thus, the variable tap on a potentiometer can be moved by finger 62. In the preferred embodiment illustrated in FIG. 2, a linear variable differential transformer 64 is mounted within and coaxial with spring 60. A non-magnetic rod 66 has its lower end attached to the movable magnetic core of transformer 64, and its upper end attached to the end of finger 62. The position of the core of transformer 64 is accordingly varied with movement of finger 62.

Using commercially available transformers one can easily obtain output signal differences of A2 volt or more as pack pressure varies from 1700 to 5800 pounds per square inch. A suitable transformer 64 is commercially available from Schaevitz Engineering, Pennsauken, N.J., as model E 300 D.

The power supply for transformer 64 is supplied through conductors in cable 68, and the output signal of transformer 64 is fed through separate conductors in cable 68 to means for repsonding to deflection of motor 36 outside a predetermined range of deflection, illustrated as meter relay 70 and alarm 72.

The stator of booster pump motor 30- can be mounted for pivotal movement about the axis of its output shaft and resiliently urged toward a reference position, in the same manner as shown for motor 36 in FIG. 2.

In the usual construction, booster pump 28 supplies more polymer to distribution passage 32 than is pumped by metering pump 34. In such a construction, booster pump 28 has a relief orifice on its output side, to discharge the excess polymer back to melt pool 26. On occasion this relief orifice becomes plugged and causes a sharp increase in pressure in passage 32. This reduces the pressure difference across meter pump 34 and causes an increase in spun denier. Conversely, if booster pump 32 suffers a loss of polymer supply due to a temporary lowering of the melt rate, the pressure in distribution passage 32 drops or becomes variable. This condition will result in production of low or variable denier yarn. Either of these conditions (plugging or the relief orifice or loss of polymer supply) causes substantial variations in the torque developed by booster motor 30'.

The apparatus as thus disclosed can provide the information disclosed in Nicholson 3,475,523 noted above. In particular, use of the present invention permits early detection of abnormal spinning conditions so that a spinning position or spinning unit can be removed shortly after actual occurrence of an abnormal spinning condition. This avoids removing for overhaul spinning positions and units run until they actually fail.

I claim:

1. In a spinning process wherein a pump supplies polymer, and wherein said pump is driven by an electric motor having a housing and a drive shaft, the improvement comprising:

(a) mounting said housing for pivotal movement about the axis of said shaft;

(b) resiliently urging said housing against the torque developed by said motor toward a reference position with respect to a fixed frame member;

(c) and detecting the amount of said pivotal movement.

2. The process defined in claim 1, wherein said pump is a metering pump supplying polymer through a filter.

3. The process defined in claim 1, wherein said step of detecting includes generating an electrical signal proportional to said movement.

4. The process defined in claim 1, wherein said step of detecting includes detecting when said movement extends beyond a predetermined range of movement.

5. A process for determining the amount of torque developed by a motor, said motor having an output shaft rotatable about an axis and a stator, said process comprising:

(a) mounting said stator for pivotal movement about said axis;

(b) resiliently urging said stator against the torque developed by said motor toward a fixed reference position with respect to a fixed frame member; and

(c) detecting the amount of said pivotal movement.

6. In apparatus for melt spinning filaments wherein a pump is driven by a motor having a drive shaft and a housing, the combination therewith of:

(a) means resiliently mounting said housing for pivotal movement about the axis of said drive shaft;

(b) and means, responsive to deflection of said motor about said axis, for detecting abnormal operation of said apparatus.

References Cited UNITED STATES PATENTS 2,566,854 9/1951 Rhodes 264-40 2,657,572 11/1953 Fann 73136E 2,741,118 4/1956 Ricciardi 73 1 0 3,104,544 9/1963 omm 73l36 0 3,166,935 1/1965 Sundt 73136 A 3,187,550 6/1965 Bratton 73 1 0 3,276,250 10/1966 German 73-136A 3,289,495 12/1966 Leto et a1 73-136 A 3,325,863 6/1967 Nicita et al. 264-176 F 3,475,523 10/1969 Nicholson 264-176 F 3,683,160 8/1972 Windley 26440 JAY H. WOO, Primary Examiner us. 01. X.R. 

